PROJECT SUMMARY (See instructions) : Chikungunya virus (CHIKV) causes explosive epidemics of mosquito-borne disease in humans, with acute febrile illness and crippling, persistent polyarthritis. Neither licensed vaccines nor effective therapies are available to protect at-risk populations. In our mouse model of joint-associated CHIKV disease, the wild-type CHIKV La Reunion (CHIKV-LR) strain caused musculoskeletal inflammatory disease while no disease was observed in mice infected with an experimental live-attenuated vaccine developed by the U.S. Army (181/25). Mechanisms underlying CHIKV pathogenesis, attenuation and immunogenicity are not well characterized, but may be linked to interferon (IFN) sensitivity. The IFN system, if activated in the absence of virus antagonism, is very effective at blocking the replication of alphaviruses and substantially ameliorating disease in animal models. Although establishment of the antiviral state is suppressed in CHIKV-LR-infected cells, arthritic disease is exacerbated In vivo when IFN-a/B and IFN-y responses are diminished, implying that disease control is at least partially due to this system. However, 181/25 may also be altered in other aspects of the host response to infection. Dendritic cells (DO), monocyte/macrophages (MO/Mphi) and osteoblasts (OB) are highly relevant to CHIKV arthritic disease and, in vitro, if an IFN-mediated antiviral state is established in these cells before CHIKV infection, virus replication is curtailed. We propose to address three major questions in these studies: i) which IFN-stimulated effectors are effective in inhibiting wild-type CHIKV-LR and by what mechanism(s) do they function; ii) is the 181/25 vaccine strain more sensitive to these effectors; and iii) do host cell response profiles distinguish vaccine from wild-type virus infections? In Aim 1, we will collaborate with the Katze Laboratory (University of Washington) using a systems biology approach to identify genes in these cell-types that are transcriptionally regulated by IFN-a/B and/or IFN-y and have potential antiviral activity against wild type CHIKV. A subtractive approach will be used to eliminate genes that are directly virus-regulated and unlikely to be antiviral as they do not protect cells. We will then test the antiviral activity of candidate effectors versus CHIKV-LR and 181/25 strains by targeted siRNA knockdown in IFN-primed or unprimed cells. Subsequently in Aim 2, we will study the point of virus inhibition by over-expression of confirmed effectors in inducible cell lines. This will also determine if the 181/25 virus exhibits enhanced induction of or sensitivity to effectors of the IFN system. Finally, in Aim 3, data will be mined to determine if there are signatures of infection associated with the host response to the vaccine that can be distinguished from the wild-type virus, such as altered regulation of inflammatory response genes, MO/Mphi activation and migration factors, or cell stress responses. Synergy with existing PNWRCE projects/ investigators will be established through collaboration, data and reagent sharing, as outlined in the proposal.